While it is a common practice to use a low-resolution liquid-crystal display (LCD) panel to display network information and text messages in a mobile device, it is preferred to use a high-resolution display to browse rich information content of text and images. A microdisplay-based system can provide full color pixels at 50-100 lines per mm. Such high-resolution is generally suitable for a virtual display. A virtual display typically consists of a microdisplay to provide an image and an optical arrangement for manipulating light emerging from the image in such a way that it is perceived as large as a direct view display panel. A virtual display can be monocular or binocular.
The size of the beam of light emerging from imaging optics toward the eye is called exit pupil. In a Near-Eye Display (NED), the exit pupil is typically of the order of 10 mm in diameter. Further enlarging the exit pupil makes using the virtual display significantly easier, because the device can be put at a distance from the eye. Thus, such a display no longer qualifies as a NED, for obvious reasons. Head-Up Displays are examples of the virtual display with a sufficiently large exit pupil.